Default language code in permalink root

I have a web store, in which I would like to have language codes displayed in all permalinks, because there are thousands of AdWords ads pointing to the website, and I wouldn’t want to use redirects because of SEO issues.

The main language of the website is not English, but now only English pages have the /en/ root. I’d like all languages to have their language code as the root, especially the main language. Is there a WPGlobus setting that I’m missing?